Aircraft condensation trails criss-crossing the sky may be warming the planet on a normal day more than the carbon dioxide emitted by all planes since the Wright Brothers’ first flight in 1903, a study said on Tuesday.

It indicated that contrails — white lines of Vapor left by jet engines — also have big knock-on effects by adding to the formation of high-altitude, heat-trapping cirrus clouds as the lines break up.

The findings may help governments fix penalties on planes’ greenhouse gas emissions in a U.N.-led assault on climate change. Or new engines might be designed to limit Vapor and instead spit out water drops or ice that fall from the sky.

“Aircraft condensation trails and the clouds that form from them may be causing more warming today than all the aircraft-emitted carbon dioxide (CO2) that has accumulated in the atmosphere since the start of aviation,” the journal Nature Climate Change said in a statement of the findings.